A comparison of virulence patterns and in vivo fitness between hospital- and community-acquired methicillin-resistant Staphylococcus aureus related to the USA400 clone

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) isolates genetically related to the CA-MRSA clone MW2/USA400 (ST1-SCCmecIV lineage) from the United States have emerged in hospitals in Rio de Janeiro and are associated with nosocomial bloodstream infections. To understand the virulence mechanisms involved in the adaptability of ST1 isolates as a hospital pathogen in Rio de Janeiro, we compared the virulence traits and fitness properties of the Brazilian isolates with those displayed by the CA-MRSA isolates from the United States. Similar to the USA400 from the United States, all the Brazilian isolates tested carried the genes encoding SEH and LukDE. In contrast, none of the Brazilian isolates carried the lukSF PVL, sea, sec, and sek genes. Competition experiments in mice demonstrated a significant increase in the fitness for the CA-MRSA isolates MW2 and USA400-0051 from the United States compared to other isolates. In the foreign body animal model, 83 % more North-American bacterial cells were recovered compared to the Brazilian ST1 isolates. Differences in gene expression of important virulence factors were detected. Transcription of rnaIII and psmα3 was increased about two-fold in the isolates from the United States, and sasG about two-fold in the Brazilian isolates. Thus, it is possible that the virulence attenuation observed among the Brazilian hospital isolates, associated with the acquisition of multiple resistant determinants, are consequences of microevolutionary events that contributed to the necessary fitness adjustment of this lineage, allowing a typically community-acquired MRSA (MW2/USA400) to emerge as a successful hospital pathogen (Brazilian ST1-SCCmecIV).

What is behind the epidemiological difference between community-acquired and health-care associated methicillin-resistant Staphylococcus aureus?

“…1 The hospital-restricted and multiresistant ST1-SCCmecIV, PVL-negative, related to the USA400 CA-MRSA-a PVL-positive strain previously detected causing CA infections in USA and Canada-emerged in Brazilian hospitals. 6 This is a good example of this epidemiological change that can even further challenge the distinction between CA-MRSA and HA-MRSA. In fact, while PVL has unquestionably been correlated with CA-MRSA, PVL alone cannot explain the CA-MRSA epidemiology because some CA infections are caused by PVL-negative CA-MRSA strains.…”

“…6 This loss may represent a compensation for fitness costs of antibiotic resistance. It is possible that this clone have evolved-during the intra-lineage diversification-to a more appropriate balance between virulence and fitness.…”

Infectious Dose Dictates the Host Response during Staphylococcus aureus Orthopedic-Implant Biofilm Infection

“…The fact that ca. 30% of individuals are carriers for S. aureus and the recent emergence of community-acquired, methicillin-resistant S. aureus (CA-MRSA) clones as causative pathogens in hospital-associated infections (19,20) highlight the importance of examining the immune response to different S. aureus strains and doses in the context of PJI. Therefore, we compared the immune responses to three distinct S. aureus clinical isolates from various epidemiological backgrounds during PJI.…”

“…S. aureus LAC is a CA-MRSA USA300 strain that was isolated from a patient with a skin and soft tissue infection (16,21). S. aureus MW2 is a CA-MRSA USA400 strain that was recovered from a pediatric patient with fatal septicemia and septic arthritis (19,22,23). S. aureus UAMS-1 is a community-acquired, methicillin-sensitive S. aureus (CA-MSSA) USA200 strain that was isolated from a patient with osteomyelitis (24).…”

Tracking methicillin-resistant Staphylococcus aureus clones in a hospital in Southern Mexico

“…[1][2][3] Surveillance of MRSA infections has shown that there are two types of strains: healthcareassociated (HA-MRSA) or community-acquired (CA-MRSA) MRSA. 4,5 The prevalence of MRSA in Mexico is high, with wide variations (24.1-80%). 6 A study carried in five hospitals of Monterrey, Nuevo León, Mexico, in 2013, detected 190 MRSA strains causing healthcare associated infection (HCAI).…”